Motor vehicles are typically used to transport people from place to place. As such they often have a passenger compartment and a power source, such as an engine that drives an automatic transmission which transmits energy from the power source to a set of driven wheels to propel the vehicle. Making such motor vehicles more efficient is currently a main focus of the automobile industry. Unfortunately, most automatic transmissions typically suffer from parasitic losses on startup of the power source. Such losses are particularly acute in the presence of low ambient temperatures, such as those present in a cold start in winter or a cold start in geographic areas having cold climates. Since the automatic transmission fluid present in the transmission has a viscosity that changes based on temperature, in cold temperature the viscosity may be quite high, thereby causing unacceptable parasitic losses and reduced fuel economy at least until the power source warms up the transmission and the automatic transmission fluid. Another problem associated with controlling the temperature of automatic transmission fluid is overheating. When a motor vehicle is subject to heavy use, for example, when the motor vehicle is towing a heavy load, the automatic transmission fluid is often heated too quickly and may overcome inherent cooling present in the transmission and additional cooling systems must be employed.
Also, in order to cool the engine, motor vehicles are typically provided with a cooling system that circulates a liquid coolant through the engine which heats the coolant and cools the engine. The coolant then flows through a heat exchanger or radiator to remove heat from the coolant. The coolant leaving the engine is often used as a heat source for auxiliary tasks. For example, the hot coolant leaving the engine may be sent though a heater core designed to transfer heat from the coolant to air. The hot air is then used to heat the passenger compartment.
To address the problem of reduced fuel economy caused by the transmission fluid being too cold soon after engine start, many motor vehicle manufacturers are pursuing technologies that will help the automatic transmission fluid heat up more quickly. One solution has been to use an oil-to-engine coolant heat exchanger to warm the automatic transmission fluid. However, in past arrangements, additional cooling has been required and therefore the arrangements have not been cost effective. Also, such arrangements have adversely affected passenger compartment heating and even adversely affected coolant flow through associated radiators. Passenger compartment heating can be compromised if too much heat is diverted to heating the automatic transmission fluid and, in the case of a two part radiator with a low temperature loop and a high temperature loop, additional efforts are needed to ensure that engine coolant is always flowing through the low temperature loop when coolant is flowing through the high temperature loop to avoid damage to the radiator.
Another solution is represented by the arrangement shown in U.S. Pat. No. 6,196,168. More specifically, a system is disclosed for preheating transmission fluid wherein part of the engine coolant is quickly heated by an internal combustion engine 17 and made available for heating of the transmission fluid as shown in FIG. 2. Coolant flows through an equalization tank 2 and then through an oil/water heat exchanger 5 but does not flow through radiator 4, 14. However, such an arrangement still suffers from several drawbacks. For example, the arrangement employs an excessive number of parts, which form a complex system that is slow to respond to changes in temperature. Another attempt to preheat transmission fluid is represented by U.S. Pat. No. 7,267,084. As shown in FIG. 2, engine coolant is sent through heat exchanger/oil cooler 24 to heat transmission fluid, however the system is not designed to send only hot or cold coolant to heat exchanger/oil cooler 24 the but rather sends a mixture of the hot and cold coolant. Furthermore, in order to function properly, the arrangement in FIG. 2 requires a relatively large number of control valves and heat exchangers yielding a relatively complicated and expensive system.
Based on the above, there exists a need in the art for a system for heating and cooling automatic transmission fluid in a rapid and efficient manner thereby reducing the viscosity of the transmission fluid and for cooling the transmission fluid when the transmission is subject to heavy loads, while overcoming some or all of the above-mentioned shortcomings of the prior art.